1. Field
The present invention pertains to means for dehumidification of containers and, more particularly, to container caps incorporating desiccant materials.
2. Prior Art
There are many and varied applications for desiccant caps intended to provide a low humidity atmosphere within an associated container. Materials requiring such protection include pharmaceuticals, seeds, food and machinery. The need for a reliable cap can be exemplified by the effect of moisture on special seeds, such as ornamental cactus seed. A relatively small bottle of these seeds may cost as much as $500. A short period of exposure to a moist atmosphere results in the sprouting and eventual destruction of the seeds. Damage is similarly incurred with many expensive pharmaceuticals when exposed to a humid atmosphere for a relatively short period of time.
A number of desiccant caps, bags and cartridges have been designed to overcome these problems as indicated by U.S. Pat. Nos. 1,425,790, 1,637,656, 1,655,248, 2,317,882, 2,446,361, 2,487,620, 2548,168 2,676,078, 3,820,309 and 3,990,872. The cap devices usually include a preforated metal holder for a desiccant which is either held together by a binder, such as asbestos, or separated from the container by a fibreglass sheet. In some cases the fibreglass is eliminated and only the preforated shield is used to isolate the desiccant from the container contents.
The results of these approaches has been inadequate. The dehumidification is short lived and the desiccant and carcenogenic materials, such as asbestos and fibreglass comingle with the container contents. The contents are often food and pharmaceuticals, making the use of such devices a serious health and product liability problem.
Attempts to avoid the use of desiccant caps by way of hermetically sealed caps embodying no desiccant have been found to be unsatisfactory. Such caps rarely provide a true hermetic seal. Even where a hermetic seal is achieved initially, the cap backs off over a period of time due to expansions and contractions of the cap caused by normal variations in ambient temperature.
In a number of prior art devices which use desiccants, an indication of the state of the desiccant cannot be determined by visual inspection, or if visual inspection is possible, the cap must be removed to make the inspection, resulting in detrimental exposure of the contents to moisture.
Some of the more sophistocated and expensive reusable caps do have humidity indicators which may be observed without opening the container, but they generally require that each individual container be picked up in order to observe the condition of the desiccant through the top of the cap, making it impractical to carry out a rapid determination of the state of humidity during shelf life.
Important disadvantages of prior art desiccator caps include high cost and the inability to have the state of the humidity rapidly determined while in storage. The inability to inspect rapidly generally increases the cost of storage, and where the cap must be opened for inspection, the storage life of the contents is appreciably shortened. The high cost of prior art devices is primarily due to the many machining operations required to produce the caps. In some cases, the expense is justified where the caps are intended for reuse. However, reuse is not practical for pharmaceuticals because of the possibility of contamination.
A prior art, low cost substitute designed to overcome the cost problem is the desiccant bar or cartridge which is simply inserted in the container along with the pharmaceuticals. Unfortunately, the bag or cartridge provide no indication of the humidity within the container and the humidity reducing capacity of such devices is limited. Where large bags or cartridges are used to extend useful life, they reduce the holding capacity of the container in proportion to their size. In addition, near sighted people have swollowed the pill sized desiccants, mistaking them for medication contained in similar sized capsules. As reported in the May 1980 issue of the Journal of the American Medical Association desiccants that are mistaken for capsules containing medication and are swollowed, result in gastrointestinal obstructions, requiring surgical removal in a number of cases.